Plasma concentrations of lamotrigine, an antiepileptic drug obtained in three adult controlled clinical trials conducted in the United States were pooled and analyzed using NONMEM, a population pharmacokinetic computer program, to facilitate development of dosing guidelines. A total of 2,407 lamotrigine plasma concentrations from 527 patients with epilepsy were analyzed. Regression equations for oral clearance were developed as a function of body size, age (18-64 years), gender, race, and use of concomitant antiepileptic drugs. The population mean apparent oral clearance of lamotrigine in adult patients receiving one concomitant enzyme-inducing antiepileptic drug and not valproic acid was estimated to be 1 mL/min/kg. Gender and age did not affect clearance significantly. On average, clearance was reduced by 25% in non-whites and increased by 13% in patients receiving more than one concomitant enzyme-inducing antiepileptic agent. Lamotrigine did not influence the disposition of phenytoin or carbamazepine. Dosing adjustments for lamotrigine in patients receiving concomitant enzyme-inducing antiepileptic drugs and not valproic acid should not be necessary for age, gender, or the number of concomitant enzyme-inducing antiepileptic drugs. Lamotrigine does not influence the dosing requirements for phenytoin or carbamazepine.

By, Thaddeus H Grasela, Jill Fiedler-Kelly, Cox E, Womble GP, Risner ME, Chen C